So, basically, what if the geopolitical divorce between the USSR and Maoist China in the late 1960's had actually escalated to war, rather than being isolated to a few border skirmishes?
Which side would be most likely to win?
From the looks of it, the PRC had a large army on paper, but i hear it was plagued by lack of experience and proper equipment, not to mention the lack of nuclear weapons. In comparison, the USSR and the Warsaw Pact had all three.
From where would the Soviet Union and associated WarPac armies attack China? I could see a massive-scale pincer movement with one army converging into the Chinese Plain from Manchuria and another crossing Xinjiang and Gansu to attack the west. Meanwhile, what sort of defensive strategies could China adopt?
Another consideration is that something like Project 571 might be slapped together by some in the PLA if things kick off.
How will associated states in Asia react?
Xinjiang seems likely to be detached from China no matter the outcome. I'm unsure as to the inclinations of the Tibetan independence movement -- could we see the Soviets sponsor a Tibetan rebellion, but one primarily socialist and detached from the Dalai Lama?
The Soviets are India's allies and are trying to appear at least somewhat conciliatory towards the west. Letting the Dalai Lama have his country back seems reasonably likely.
I'm also very curious about the possible stance of North Korea and Vietnam.
I could see the Red Army rushing to Pyongyang after securing Manchuria to keep South Korea and their American patrons from getting any funny ideas.
Restating that North Korea is under their nuclear umbrella is probably sufficient.
Vietnam, meanwhile, could be affected by her sponsor states fist-fighting each other to the north -- could this mean that South Vietnam survives in the Mekong Delta region? I doubt Saigon could hold on to the pre-war equal division of the country, considering that the Tet Offensive already happened a year before, too.
Tet wiped out the offensive capabilities of the NLF. The fall of South Vietnam came pretty much entirely via the conventional operations of the NVA, which has now lost almost all its arms imports (which it was really dependant on as seen in 1973 when mining a single harbour brought the country to the negotiating table). South Vietnam meanwhile has a lot more breathing room, and so Vietnamization is probably properly implemented.
Better question is if the US can justify pulling out when a literal apocalypse is brewing a little to the north.
Would the RoC in Taiwan make a second try at Project National Glory?
Good chance of it.
What about India? Would they see this as an opportunity to solidify their claims on Aksai Chin and Arunachal Pradesh?
Absolutely, as well as to reignite Tibetan resistance.
What would be the long-term geopolitical effects?
Soviet attention and funds would have to be strictly diverted to the war with China, which could hamper their ability to fund far-left insurgency movements in the "third world". On the other hand, eliminating Maoism as a competing, sometimes American-friendly ideology could serve Soviet objectives well. Any thoughts on how the dynamics of the Cold War would change?
That was the case only after Nixon and Mao became BFFs. Prior to that it was Mao that was pressing the hardest for the expansion of Communism by military force. And after that the Soviets became more aggressive as to compete with China.
Tensions would run higher than at any point in OTL during the liquidation of China, but in the long term East-West relations might be more stable.
What are the effects on China in specific?
Lin Biao could be propped up as a pro-Soviet satrap in China in case of Soviet victory, but how stable would his position really be?
Depends on if the country was nuked before he comes to power.
Would China still enact economic reforms like OTL's?
Probably not if its a glowing parking lot.
It seems like it'd depend on who's lucky to survive the imminent purges of Mao or the following purges of the Soviet occupation force, but would the Soviets try and prop up China's command economy?
They would "try". A better question is if they honestly do all they can or if they make a show of some token efforts.